Grapes are the most significant raw materials during the winemaking process. A good understanding of grape composition is vital in understanding the process of winemaking as well as making better quality wine. Grapes are made of chemical and physical properties, as discussed below.
Physical Composition
The fruit of the grape is a berry, and a berry is attached to the stem. Many berries form a bunch of grapes. The essential parts of the berry are the seeds, pulp, and the skin. The skin is the outer most layer covering the berry, which renders the berry waterproof.
The skin is made up of tannins, coloring matter, potassium, and aromatic substances. Below the surface lies the pulp with large vacuoles containing the juice. When the berry gets crushed, the fragile cells in the pulp are broken, and the fluid is released, which is commonly known as the free run. At the center of the flesh, seeds are delocalized, and the berries contain about two to four seeds. During the fermentation of red wines, tannin is extracted from the seeds.
Chemical Composition
Freshly extracted grape juice consists of about 70 to 80% of many dissolved solids and water. The dissolved solids include various organic and inorganic compounds. The organic and inorganic compounds are organic acids, aroma compounds, sugars, pectic substances, nitrogenous compounds, minerals, and phenolic compounds. Fructose and glucose are the main sugars in the juice. Sugar content in ripe grapes varies between 150 to 250g/L. Next to sugars are the organic acids that are responsible for the taste and tart.
Further, they have a marked influence on pH, color, and stability of wine. Phenolic compounds are vital in determining the flavor and color of the wine. Nitrogen compounds play an essential role since they serve as nutrients for yeast and lactic acid bacteria. Many volatile odorous compounds found in wine are derived from three primary sources: fermentation, grapes, aging, and maturation. Minerals are taken up from the soil by the vine, and they account for about 0.2% to 0.65% of the fruit’s weight. Lastly, pectic substances act as cementing agents in the cell wall, and during ripening, they are hydrolyzed by pectolytic enzyme, which renders the berry softer as it ripens.
